This invention relates to the molding of rubber. In particular, the present invention relates to injection molding of rubber for rubber-soled footwear and especially to injection molding of a two-color rubber soled footwear construction.
The present invention constitutes a further modification of the method and apparatus described in copending U.S. patent application Ser. No. 729,570, filed May 16, 1968 and assigned to the assignee of the present invention, now U.S. Pat. No. 3,608,004 issued Sept. 21, 1971. The latter patent application is hereby incorporated herein, by reference, in its entirety.
As was noted in said co-pending application difficulties are encountered, particularly when making soles with two differently colored rubber materials, in achieving a sharp, well-defined boundary between the foxing and the outsole, because of the difficulty in preventing the first-injected foxing rubber from undesirably mixing with the second-injected outsole rubber.
It is, therefore, an object of the present invention to provide a modified method and apparatus which is capable of achieving a clean, sharply-defined junction between the outsole and the surrounding foxing.
It is a further object of the present invention to provide a method and apparatus of the type described above which is capable, prior to injection of the second color rubber material, of automatically removing the "flash" resulting from the first injected rubber from the region of the mold in which undesired intermixing of colors might occur. It is also an object of the present invention to provide a method and apparatus for easily and economically removing the "flash" resulting during rubber molding.
With respect to those features of the present invention which are substantially identical to corresponding features described in said co-pending application reference should be had to the latter application for more detailed explanation. In this connection it will be noted that corresponding parts in this and in said co-pending application have the same reference numberals.
According to one embodiment of the present invention a first rubber for the foxing and midsole is injected into a mold cavity in which a movable sole plate spreads the injected first rubber against the underside of a lasted upper. The pressure required for this spreading operation unavoidably results in some rubber, in the form of "flash", escaping around the periphery of the sole plate. The sole plate is provided at its periphery with a circumferential lip extending toward and into close proximity to the side mold rings within which the sole plate moves. A circumferentially extending groove, provided below the lip, collects some of the flash rubber which escapes past the lip during the first spreading operation. After this first rubber has set sufficiently to provide a clean retraction of the sole plate without any sticking of the first-injected material thereto, the sole plate is retracted away from the midsole to form between itself and the mid sole a mold cavity suitable for injection of the second, i.e. outsole rubber. During this retraction, the portion of the first injected rubber collected in the peripheral groove of the sole plate is forced to move with the latter thus being torn from the remainder of the first injected rubber along a predetermined peripherally extending line, i.e. along the line formed by the outwardly extending lip and thus being the thinnest and therefore weakest region of the downwardly depending flash rubber. After the "flash" resulting from the first injection is thus severed and moved out of the way by the sole plate, the second rubber is injected into the mold cavity. Substantially all of the flash of the first injected rubber is thus removed automatically from the region of potential intermix prior to injection of the second rubber. The sole plate is then again advanced toward the lasted upper to spread the second, i.e. outsole-rubber against the midsole-rubber to be vulcanized thereto.
The configuration of the sole plate is such that the "flash" which is necessarily formed by some of the first rubber escaping intermediate the sole plate lip and the side rings in which the sole plate moves, is collected in the peripheral groove which extends around the sole plate at the underside of the lip. The portion of the flash rubber collected in the groove is formed therein into the shape of a bead.
By tearing the peripherally extending bead portion from the foxing during the aforesaid retraction of the sole plate not only is most of the flash removed but access to the second injection port is cleared of any overhanging flash of first injected rubber and the mold is thus automatically ready for the second injection. During the second upward movement of the sole plate for applying the second injected rubber outsole against the midsole, the rubber bead which is still located in the peripheral groove of the sole plate is once more entrained to move therewith thus substantially preventing the second injected flash rubber from escaping between the sole plate and the side rings past the region of the peripheral groove.
With this construction and method it has been found that intermixing of the outsole material with the foxing material at the outsole-foxing junction is substantially eliminated. Any intermixing which does occur, using the process of the present invention, is restricted to regions below what will ultimately (i.e. after trim) be the lowermost portion of the downwardly depending foxing material i.e. such intermix is restricted to the region below the plane at which trimming takes place. There is thus assured a clean, sharply defined junction line between the outsole and the foxing. It is, therefore, possible to manufacture a two-color rubber sole structure in a highly efficient manner with the method and apparatus of the invention.